Transistors are key components of modern integrated circuits. To meet the requirement of increasingly faster speed, the drive currents of transistors need to be increasingly greater. Since the drive currents of transistors are proportional to the gate widths of the transistors, transistors with greater widths are preferred.
The increase in the gate widths of the transistors, however, conflicts with the requirements of reducing the sizes of semiconductor devices. Fin field-effect transistors (FinFET) were thus developed. By forming fins that act as the channel region of the FinFET, the drive currents of the transistors are increased without the cost of occupying more chip area.
The FinFETs, however, also suffer from drawbacks. With the increasing down-scaling of FinFETs, the increasingly smaller sizes of the fins result in the increase of the resistances in the source/drain regions, and hence the degradation of device drive currents. The contact resistances between the contact plugs and source/drain silicide regions of the FinFETs are also increased due to small fin areas. Additionally, it is difficult to form contact plugs connected to source/drain silicide regions of the FinFETs. This is because the fins of the FinFETs have small areas, the landing areas for the corresponding contact plugs are thus small. The process window for landing contact plugs accurately on fins is also small, which means that there is little room for the process variations to occur without affecting the reliability of the resulting FinFETs.